This project involves the study of the biology of Entamoeba and Trichomonas. The amebal toxic study continues to attempt to purify the toxin and identify the nature of its lectin-like activity. The toxin is neutralized by purified IgG from sera of patients known to have had invasive amebaisis with a general antiamebal antibody response, but not by IgG from sera of control individuals. Studies on selecting and maintaining virulent subpopulations of relatively avirulent amebal strains has been completed after more than 2 years and is being prepared for publication. Recently a sensitive animal model for Giardia lamblia infection has been found in the newborn mouse inoculated intragastrically. A study of Tritrichomonas muris revealed excretion of many viable pseudocysts in the feces of pregnant and lactating hamsters and the early infection of the newborn. A major project on Trichomonas vaginalis in collaboration with a grant supported study at the University of Massachusetts and Johns Hopkins University has been initiated.